Cathode-ray type of electron discharge device



Dec. 25, 1951 s n- 2,580,250

CATHODE RAY TYPE OF ELECTRON DISCHARGE DEVICE Filed July 29, 1950 6SOURCE OF DEFLECTON wlhwllwm Inventor:

Henry Hi8 Attor ey Patented Dec. 25, 1951 Fries OATHODE-RAY TYPE OFELECTRON DISCHARGE DEVICE Henry M. Smith, Schenectady, N. Y., assignorto General Electric Company, a corporation of New York Application July29, 1950, Serial No. 176,750

This invention relates to electron discharge devices of the type inwhich electrons are caused to produce images on luminescent screens and,in particular, relates to cathode ray electron discharge devices of thekind used for purposes of projection of pictures in television receiversor for producing oscillograms.

It is known that in order to obtain a sufiiciently intense indication onthe screen of a cathode ray electron discharge device it is necessary toimpart high velocities to the electron beam which produces light on thescreen. However, increasing the velocity of the electron beam byincreasing the anode voltages which accelerate the beam gives rise tocertain problems. If conventional beam'deflection circuits are employed,the electron discharge device has low deflection sensitivity; that is,since the electrons in the beam are moving faster, it takes a largerforce to produce the same absolute deflection that would be producedwith a lower velocity electron beam. In addition, a special design isrequired for the electron gun when high potentials are used on thevarious anodes. In a magnetic deflection cathode ray electron dischargedevice insulation of the second anode coating in the device from thedeflection coil may present a serious problem when high potentials areused on the second anode.

Heretofore it has been proposed to interpose a shielding grid of thekind shown in U. S. Patent 1,810,018 between the luminescent screen ofthe cathode ray type of electron discharge device and the remainder ofthe electrode structure of the device. With this innovation it ispossible to utilize a conventional deflection circuit in the electrongun portion of the device while at the same time achieve the advantagesof a high velocity beam. It will be noted that with this arrangement thescreen is operated at a much higher potential than the shielding grid. Acathode ray type of electron discharge device of the kind just describedwith a shielding grid has the disadvantage that the screen of the tubeis subject to background illumination for reasons to be hereinafterdescribed. It is to the solution of this problem of backgroundillumination that the present invention is particularly addressed.

Accordingly, it is an object of my invention to provide means in cathoderay type of electron discharge apparatus whereby the advantages of a"high velocity beam may be combined with the advantages of highsensitivity deflection circuits without the serious limitations ofdevices combining these features.

9 Claims. (01. 315-1) It is another object of my invention to provide acathode ray tube in which the advantages of high deflection sensitivityand high intensity illumination are present without the seriousdisadvantage of background illumination.

It is a further-object of my invention to provide improvements incathode ray electron discharge apparatus.

The features of the invention desired to be protected are set forth inthe appended claims. The invention itself, together with further objectsand advantages thereof, may best be understood by reference to thefollowing specification taken in connection with the accompanyingdrawing in which is shown a cathode ray type of electron dischargedevice, in section, connected in a manner to carry out the objects of myinvention.

Briefly stated, the objects of the invention are achieved in oneexemplary embodiment by providing a collector electrode or means behindthe grid of the cathode ray type of electron discharge device andoperated at a slightly higher potential than the shielding grid tocollect the stray electrons which produce the background illumination ofthe luminescent screen.

Referring now to the single figure of the drawing, there is shown acathode ray type of electron discharge device I having an hermeticallysealed envelope 2. At one end of the envelope is located a cathode 3supplying electrons for the device I. At the other end of the device Iis located a lumi nescent screen 4 which is subject to the bombardmentof the electrons from the cathode 3. In: termediate the cathode 3 andthe screen 4 are located various electrodes entirely conventional in theart for the purpose of forming and focussing the electron beam. Coil 5afunctions to deflect the beam in accordance with external signals.applied by a source 6. A shielding grid electrode l is located a shortdistance from the screen i'which is operated at a much higher potentialthan the grid 7 so that in efiect the cathode ray device to the left ofthe grid '1 operates substantially as a conventional low voltage cathoderay device. It will be appreciated that electrons from the cathode 3will be easily deflected by the deflection means 6 because they are oflow velocity, and upon passing through the grid 1 the electrons will beconsiderably accelerated and consequently will strike the screen 4 ofthe tube With high. energy thereby producing large amounts of light fromthe luminescent coating making up the screen 4. It is readilyappreciated that by the provision of the grid 1 the advantages of a highdeflection sensitivity device with a device that has high luminositycharacteristics is achieved. 7

It will be noted that not all of the electrons will pass through thegrid structure to the screen.

- Some of the electrons will impingeon the wire mesh iori'nin'gthegrid'l'with the-consequent liberation of secondary electrons. When theelectrons reflected and liberated from the shieldin grid 1 pass in thevicinity of the open spaces of the shielding grid electrode 'L'the'ywill be attracted through and strike the screen 4 thereby producingbackground illumination on the screen.- It will be appreciated that this-b'ackground illumination is of a shape corresponding to the shape ofthe grid. Background illumination may be eliminated by eliminating theelectron cloud formed behind the grid. I have provided in one embodimenta collector electrode 8 for this purpose. The-collector electrode 8-is-operated at a potential slightly higher than-the. potential of thegrid "electrode '1. Preferably the second anode!) is operated at apotential slightly higher than collector eleotrodeB to insuresubstantially complete collectionof all stray electrons. It will :bereadily appreciated that the-second -anode 9 may be utilized as acollector electrode as well. When the-second anode '9 is used asa'collector it would be necessary -to operate'the-seoond anode 9 ate.potential slightly higher than-the shielding grid electrode 1. Aseparate collector electrode may be thus eliminated. The collectorelectrode 8 and the second anode 9 may be connected together andoperated at thesame potential slightly higher than the grid electrode'5.

Referring now to the particularities of construction of the cathode raydevices of my invention, there is shownin the drawing a conventionalelectron gun for the device comprising a cathode 3, an intensity-controlelectrode lfl, and a first anode electrode II. The deflection coil 5a,entirely conventional, iunctions to deflect the electron beam from theelectron gun in-response to a deflection signal. It is understood ofcourse that the electrongun-maybe focussed magnetically orelectrostatically and likewise that the beam deflection maybeaccomplished either-by electromagnetic or electrostatic means. "In thefigure c0115 functions to'focus the electron beam. The second anode 9comprises athinconduotive coating extending into the-neckofthe device Ias shown. This conductive coating is usually-an aquadag coating,talthough o-f course other suit-. abl'e materials maybe employed. Thegrid of the device I is attached to a metalring I 2 suitably fastenedto'one end of theglass cylinder I3.

The other end of the glass cylinder I3 is connected 'totlie 'body'of'the glass envelope -2. The attachme'ntof the'irisulatin'g cylinder [3to the body of theenvelo'pe 2 at alocatio'n rem'oved'from the screen 4reduces the surfa'oe'voltage gradient between grid 1 and screen dthereby elimlnating the danger of' eleotrical'breakdown between thesehigh voltage electrodes. On the'inside'surface of the glass cylinder l3,and fla"short"distan'ce behind the "grid 1 is located aconductivestrip'which'may be formed ofaqua'dag or any'dtner suitablemate-- rial. Conductorsl' l and icpermitthe'application of externalpotentials to the grid 1 and electrode 8 respectively.

The grid l is made'of'a fine mesh o'fwir'es, for instance, a tungstenring strung with .001-or an inch tungsten wire wound 330 turns .per inchwould be suitable. 'Inthe preceding example the grid then would comprisea series of .001 of an iparent glass base.

screen by the usual techniques. 'ran'gement has the known advantage ofhigher the grid 7.

"adapted to be-excited by-anelectronbea'm. The

screen 4 may be formed on a conducting trans- Also, a conductivealuminum film could be applied over the phosphor of the This latterarlight output because of light reflection from the aluminumfllm. Thealuminum film also has the advantage that it helps to prevent any looseparticles of phosphor from coming oil and getting on A conductiveconnection I6 is made through the glass envelope so that the screen maybe externally energized by suitable potentials.

Referring -.-now to :the operation of I one of the above describedembodiments ofmy inventiomthe cathode Sis connected'to oneend-of .a'suitab'le source H of unidirectional potential. The screen It isconnected to the highpotential end ofthe unidirectional source.Thesecond anod'e'9 is connected to atpotentialpoint intermediate the:potential applied between the cathode and the screen anode [-4. Thecollector electrode Bisconnected to a potentialpoint on theunidirectional source -l'.' which is-slightly higher than thesgrid "ibut slightly less .positiveor the samelipo'tential as-the secondanode 9.Electrodes 10 and H are connected to suitablepotential points: onthe-uniw directional source 1 i. .:If the beam current to bemodulatedthecontrol grid 10 mustor'course be connected to-a modulatingpotential source. The defiectioncoils Saarec-onnectedtoa source ofdeflection signal =6. With the second anode operating at-a potential ofabout 10,000'=volts,"with the screen 4 operating at -apotential of about45,000 volts, with the shieldinggridl operatingsat a potential-anywherein the range of -300 volts lower than the second anode "9 andcollectorelectrode 8, very satisfactoryoperationof "the devicewasobtained. Background illumination was virtuallyeli-minated.

Advantages in the use of cathode ray tubes of the-type described aboveare that the conventional low voltage ele'ctronrgun andelectro'static.ormag'- netic deflection system of low ipower 'canbe-used. A further advantage is that no extra insulation in the neck ofthe c-athode ray devi'ceslisrequired for high -voltage operation.Furthermore, neither the beam focus nor deflection are afiected'lby thepotential of thefluo-r'esc'ent screen; consequently, a highvoltage-source of relatively 10W spo'w-er-"capabilities can be usedforthe application of potentials -to-=the luminescent screen.

-Whil=e I have shown and described particular embodiments 'of myinvention, it will be obvious to those skilled in the art "that variouschanges and modifications may be made 'withoutdeparting -from myinvention inits broadaspec'ts and therefore, airs in "the appendedclaims to "cover all suoh changes"and modificationsas fall'within thetrue scope of "my invention.

Wh'at I claim as *new' and desire *to secureby Le tors Patentin t h'eU'nite'd States is:

1. Cathode ray electron discharge "apparatus, comprising a cathode ra'ytype -of -electron tlis charge de'v-ice craving a cathode, a luminescentszreen a'node, a second anode located between said cathode and saidscreen anod'e, an lectrode mounted between said second anode and saidscreen anode adjacent to said screen anode, means for maintaining saidelectrode at a slightly lower potential than said second anode and meansfor maintaining said screen anode at a considerably higher potentialthan said second anode.

2. The apparatus of claim 1 which said electrode comprises a fine meshwire screen located substantially parallel to the face of the cathoderay electron discharge device.

3. The apparatus of claim 2 in which said second anode comprises aconductive ring located on the inside surface of the envelope of saidelectron discharge device.

4. Cathode ray electron discharge apparatus, comprising a cathode raytype of electron discharge device having a cathode, a luminescent screenanode, a second anode located between said cathode and said screenanode, said second anode comprising a conductive coating on the insidesurface of the envelope of said cathode ray electron discharge device,an electrode mounted between said second anode and said screen anode andadjacent to said screen anode, a second electrode located between saidfirst electrode and said second anode, means for maintaining said firstelectrode at a slightly lower potential than said second anode and saidsecond electrode, and means for maintaining said second anode at aslightly higher potential with respect to said second electrode, andmeans for maintaining said screen anode at a considerably higherpotential than said first electrode.

5. The apparatus of claim 4 in which said first and second electrodesare located on a cylindrical insulating member attached to the envelopeof said electron discharge device at a location substantially removedfrom said screen anode, said first electrode comprising a wire meshattached to the free end of said cylindrical member and locatedsubstantially parallel with respect to said screen anode, said secondelectrode comprising a conductive ring on the inside surface of saidinsulating member.

6. The apparatus of claim 5 in which means are provided for maintainingsaid second anode and said second electrode at substantially the samepotential.

7. Cathode ray electron discharge apparatus, comprising a cathode rayelectron discharge device having a cathode, a luminescent screen anode,a second anode located between said cathode and said screen anode, saidsecond anode comprising a conductive coating on the inside surface ofthe envelope of said cathode ray electron discharge device, an electrodemounted between said second anode and said screen anode and adjacent tosaid screen anode on a cylindrical insulating member attached to theenvelope of said electron discharge device at a location substantiallyremoved from said screen anode, said electrode comprising a wire meshattached to the free end of said cylindrical member and locatedsubstantially parallel with respect to said screen anode,

means for maintaining said first electrode at a slightly lower potentialthan said second anode, and means for maintaining said screen anode at aconsiderably higher potential than said first electrode.

8. Electron discharge apparatus comprising a cathode ray type ofelectron discharge device having an electron gun, a luminescent screen,electron beam deflecting means, a first electrode mounted near saidscreen, a second electrode mounted adjacent to said first electrode onthe gun side of said first electrode, means for maintaining said secondelectrode at a slightly higher positive potential than said firstelectrode, means for maintaining said screen anode at a considerablyhigher potential than said first electrode, whereby high intensityillumination free of background illumination is produced on said screenwhile at the same time high deflection sensitivity is obtained.

9. Electron discharge apparatus comprising a cathode ray type ofelectron discharge device having an electron gun for developing acathode ray beam, a luminescent screen adapted to be excited by saidcathode ray beam, electron beam deflecting means in operativeassociation with said cathode ray beam for deflecting said cathode raybeam, an electrode mounted near said screen, said electrode comprising awire mesh located substantially parallel with respect to said screen,another electrode mounted adjacent to said first electrode on the gunside of said first electrode comprising a conductive coating on theinside surface of the envelope of said discharge device, energizingmeans for energizing said electron gun and said electrodes so that thedeflection sensitivity of said cathode ray beam is high, energizingmeans for energizing said luminescent screen so that high intensitylumination is produced by the impingement of said electron beam on saidscreen, said second electrode adapted to be energized with a slightlyhigher positive potential than said first electrode while said screen isadapted to be energized by a substantially higher potential than saidfirst electrode.

HENRY M. SMITH.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,810,018 Howes June 16, 19311,955,899 Zworykin Apr. 24, 1934 2,077,270 Schlesinger Apr. 13, 19372,239,769 Batchelor Apr. 29, 1941 2,289,906 Epstein July 14, 19422,315,367 Epstein Mar. 30, 1943 2,461,515 Bronwell Feb. 15, 19492,483,457 Feldt et a1 Oct. 4, 1949 2,518,200 Sziklai et a1 Aug. 8, 19502,543,477 Sziklai et al Feb. 27, 1951

